Engine driven generator sets are used for a wide variety of purposes. Those which operate using a combustion engine as the power source are prone to vibrations associated with the impulse stroke of the engine. FIG. 1 illustrates this initial torsional impulse due to cylinder firing during the operating cycle of a typical single cylinder four cycle engine operating at full load. The peak torque generated by the engine is about 18 times the average torque over the engines' rotational crank cycle of 720 degrees.
A typical engine driven generator set 200 housed within a housing 205 is illustrated in FIG. 2. The housing 205 is mounted to an application structure 207 using mounts 209. In some embodiments, the mounts 209 are soft mounts (such as springs, rubber mounts, etc.), and in other embodiments the mounts 209 allow for the housing 205 to be rigidly mounted to the application structure 207. The application structure 207 can be any structure a generator set could be mounted to such as, for example, a vehicle (i.e. car, boat, RV, etc.) or the ground.
The generator set 200 can be either a fixed speed generator set or a variable speed generator set. The engine driven generator set 200 includes an engine component 210 coupled to a flywheel 215 and has rubber mounts 212 that mount the engine component 210 to the housing 205. The flywheel 215 is typically used to smooth the rotational speed variations of an engine by storing the engines power stroke energy in the rotational inertia of a large generally cylindrically shaped mass and releasing that energy until the next power stroke. The generator set 200 typically also contains a machine 220 which converts the rotational energy of the engine and flywheel 215 into electricity and vice versa. In some embodiments the machine 220 is mounted to the flywheel 215. The generator set 200 also includes a rectifier 225 coupled to the machine 220, DC filters 230 coupled to the rectifier 225, and a direct current to alternating current (DC to AC) inverter 235 coupled to the DC filters 230. The alternating current (AC) produced by the machine 220 then is rectified to direct current (DC) by the rectifier 225 and runs through the DC filters 230 which provide a more uniform voltage output, and the DC to AC inverter 235.
Even though the flywheel minimizes rotational speed variations, it does not address the induced torque of the cylinder block and its transmitted vibration through vibration isolation mounts to the final application structure. The transmitted vibration is particularly high at low engine speeds when single and twin cylinder engines are used. It is desirable to operate at low speed to minimize noise levels, and even while operating at zero load, at low speeds vibration is a significant problem.
In addition to input power induced vibrations, the level of vibration in a generator set is also a function of the amount of load or power draw from the generator's stator. Consequently the amplitude and frequency of the resultant vibration is both a function of engine speed and power draw from the generator set. In current practice, the machine draws a torque from the engine crankshaft independent of when the torque is produced in the engine.
Also, traditional four-cycle combustion engines, whether using spark or compression ignitions, develop power in pulses. These power pulses can span more than ten times the engine's average output power and cause the application structure holding the engine to roll back and forth. Typically, these engines are softly mounted so only a fraction of these pulsations are transmitted to the application structure.
In addition, some engines utilize internal rotating counterbalancing shafts to help offset the imbalances of the crankshaft and piston, and these imbalances produce additional couples and periodic rotational vibrations.
The resultant vibrational problems have been primarily dealt with by placing the generator set on elastic mounts which serve to isolate the generator set vibrations from the application structure. Such mounts, however, do not effectively address the severe vibrational levels which can occur, especially during low engine rotational speeds and while large current draws are taken from the generator set.
What is needed is a generator set which can produce power without the vibration issues associated with systems, even when operating at low speeds or while operating under large power draw conditions.
The present disclosure discloses a generator set which solves many of the problems associated with existing generator sets. It will be appreciated that the disclosure may disclose more than one embodiment. The embodiments are pointed out with particularity in the claims annexed hereto and forming a part hereof.